Lignocellulosic biomass is an abundant source of fermentable sugars, and biofuels derived from these renewable sources represent one of the best alternatives to petroleum-based fuels. Efficient conversion of lignocellulosic biomass, however, remains a challenge due to its inherent recalcitrance. Given the current state of technology of simultaneous saccharification and fermentation (SFF) and the commercial enzyme cocktails available, various chemical and thermal pretreatment steps are required to achieve meaningful conversation of biomass. Another alternative seen as viable and cost competitive for the future is consolidated bioprocessing (CBP), in which case saccharolytic enzyme are produced by the CBP organisms, which also ferment sugars released from biomass to the end product.
In nature, most cellulolytic organisms are of two types: those with non-complexed cellulases, xylanases, and hemicellulases produced by aerobic fungi and most bacteria; and those where cellulases, xylanases, and hemicellulases are complexed on a protein scaffold. This latter case is known only for a few anaerobic bacteria and fungi. In both cases, the enzymes secreted have a wide range of complexity but are mostly equipped with a single catalytic domain. An alternate enzymatic system, midway between the two previous paradigms, is one where the most abundant enzymes secreted are not only multi-modular but possess more than one catalytic domain. This strategy could present several advantages; it allows the synergistic effects between several catalytic domains usually found in cellulosomal systems but also lessen problems that cellulosomes may encounter due to their size.
The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.